WASHINGTON – A slide projected onto the wall at the American Israel Public Affairs Committee gathering Monday contained a warning to delegates: “AIPAC is Bipartisan,” it said, next to an image of a Democratic donkey and Republican elephant in boxing gear. “Check your gloves at the door.”

They checked their gloves, all right — but less to practice bipartisanship than to pummel the Obama administration with bare knuckles. In the brawl between President Obama and Israeli Prime Minister Benjamin Netanyahu over Iran nuclear negotiations, AIPAC has joined congressional Republicans in siding wholeheartedly with the Israeli hard-liner.

The rift with Obama is nothing new; four years ago, AIPAC delegates were urged not to boo Obama when he spoke to the group (most obeyed). But this situation is worse, because Netanyahu, by accepting House Speaker John Boehner’s invitation to address Congress — snubbing Obama, who wasn’t consulted — is exploiting a partisan rift in American politics and driving a wedge through the American Jewish community. And congressional Republicans, by giving Netanyahu their pulpit 14 days before Israel’s elections, are brazenly taking sides in that country’s politics. This all is likely to backfire by firming Democratic resistance to more Iran sanctions — and, in the long run, by politicizing U.S.-Israeli relations.

The AIPAC delegates left no doubt where they stood as they listened to speeches by Netanyahu and by an Obama administration representative, U.N. Ambassador Samantha Power. The transcript will show that they applauded Netanyahu 59 times in his 22-minute speech, compared with 34 times during Power’s 30-minute address. But that doesn’t reflect the rapturous nature of the reception for Netanyahu (who got an 80-second standing ovation) and the polite but tepid response to Power (who received a perfunctory 18 seconds).

“As a few of you may have heard, the prime minister of Israel is in town,” Power said with a smile. There was laughter — and then a wave of defiant applause swelled across the room. Power aimed for the high ground, saying that the “U.S.-Israel partnership transcends politics,” but only about half the crowd lumbered, slowly, to their feet at this obligatory applause line, while others sat with arms folded.

Thirty minutes later, Netanyahu asserted that “my speech is not intended to show any disrespect to President Obama or the esteemed office that he holds” — but curiously, only about one in 10 stood to applaud.

“My speech is also not intended to inject Israel into the American partisan debate,” Netanyahu continued, noting that the alliance “has been championed by both parties and so it must remain.” Roughly the same percentage stood to applaud this sentiment.

AIPAC delegates had to be warned to be nice to Power. A slide flashed on the wall featured Casper the Friendly Ghost and the message: “Don’t boo! Be Friendly.” Just before Power took the stage, the announcer admonished attendees to “be sure to treat all of our speakers and fellow delegates as guests in our home.”

Power read a too-long speech that included a couple of Hebrew words and made all the usual references to the Holocaust, her trip to Israel and Jewish culture. But no more than one-fifth of participants stood when she vowed that “the United States of America will not allow Iran to obtain a nuclear weapon — period.” And, in truth, her boasts about her achievements for Israel (helping “secure for Israel permanent membership in what’s called the Western European and Others Group”) were modest.

She was no match for Netanyahu, a head of government and a gifted orator whose politics are more in tune with AIPAC’s. They politely applauded when he acknowledged the presence of Dan Shapiro, the U.S. ambassador to Israel, but they gave a huge ovation to Ron Dermer, the Israeli ambassador to the U.S. who has been active in Republican politics.

They gave a boisterous standing ovation to Netanyahu’s invocation of a “moral obligation” to give his views on the Iran negotiations, declaring an end to “the days when the Jewish people are passive in the face of threats to annihilate us.”

The Israeli leader put his spat with Obama in the context of previous disagreements back to 1948, arguing that “disagreements in the family are always uncomfortable, but we must always remember that we are family.”

That’s true. But when family members start meddling in each other’s domestic affairs, they risk estrangement.